Find the curve of shortest length between points (R0, 0, Z0) and (R1, Φ1, Z1) on the conical surface r = z tanα, where (r, φ, z) are cylindrical coordinates and α, the opening (half) angle of the cone, is a constant. Recall that the increment of length ds in cylindrical coordinates is given by ds2 = dr2 + r 2 dφ2 + dz2

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?